Stable oil-in-water emulsions are very difficult to separate and represent one of the most difficult problems encountered in petroleum production. The viscosity of the emulsion is much higher than that of the separated phase, which is the reason for high wellbore pressure drop and low oil recovery. This paper is about a laboratory study of the use of ultrasonic energy to enhance the separation of a suspended oil phase from an aqueous medium.
This paper investigates the effect of ultrasonic energy on the separation of oil and water in stable oil-in-water emulsions. It was found that the oil phase concentration, oil phase composition, ultrasonic intensity and temperature are the key factors affecting the emulsion coalescence, and the emulsion coalescence occurred in a relatively short time after ultrasonic treatment. In addition, the oil droplets had a higher oil phase composition (10%, 35%), which may explain the reduction of residual oil observed in past research work. A number of photomicrographs of the dynamic coalescence process were taken and the change in average droplet size was recorded. This led to the development of a mathematical model of the rate of coalescence as a function of ultrasonic frequency, oil phase concentration, and other variables. These models are theoretically sound and easy to use. Comparison of mathematical model predictions with experimental results provides good agreement.
The results of the study show that sonication at an optimal energy level is superior to certain chemical flocculants in improving liquid-liquid separation performance. This technology can also be applied to post-emulsion separation and on-site wellbore treatment.
Oil-in-water emulsions are important in various stages of drilling, completing and producing oil wells. Oil-water emulsions exist, either in the reservoir itself or as a result of the extraction process. These emulsions greatly increase the cost of transportation and refining, and actually add to wellbore and reservoir problems.
Emulsions have traditionally been considered an irreversible but integral stage in oil production. The most important properties of these emulsions include particle size and distribution, viscosity, density, concentration, oil and carbon content, sound velocity, pH, potential and surface charge, etc. With the values of these parameters, emulsions can form or break. However, in most cases of petroleum engineering applications, it is necessary to destroy these water-in-oil emulsions.
Use of Ultrasonic Energy and Emulsions
Demulsification is the emulsion breaking process that involves the coalescence of small oil droplets to form larger oil droplets. In order to speed up the coalescence process and increase the recovery factor, some additional force is required. Several techniques exist for enhancing demulsification. Typical additions found in the literature include chemical demulsifiers, pH adjustment, gravity or centrifugal settling, filtration, heat treatment and electrostatic demulsifiers. Ultrasonic technology has the ability to rapidly break emulsions and this technique can be used to analyze emulsions non-destructively. Also useful for breaking up emulsions to improve oil recovery and increase grease production. Effects of Ultrasonic Irradiation on Coalescence and Separation of Crude Oil-Water Emulsions. Through experimental studies, they found that the combined effect of ultrasonic and chemical treatments greatly enhanced the separation efficiency of chemical treatments exposed only to low-frequency mechanical agitation. They concluded that sonication technology offers a potentially practical way to improve natural oil-water coalescence and separation while reducing chemical requirements.
Ultrasonic Devices for Efficient Emulsification
RPS-SONIC offers a broad range of ultrasonic devices and accessories for the efficient emulsification and dispersing of liquids.
1.Laboratory ultrasonic devices of up to 500 watts power allow for the easy preparation of emulsions in test-tubes, Eppendorf vessels, beakers or flow cells. These devices are mainly used for sample preparation or initial feasibility studies and are available for rental.
2.800 and 1,000 and 2,000 watts ultrasonic processors like the RPS-SONO20 set with flow cell and various booster horns and sonotrodes can emulsify larger volume streams. Devices like this are used in the optimization of the parameters (like: amplitude, operational pressure, flow rate etc.) in bench top or pilot plant scale.
3.Industrial ultrasonic processors of 3, 6, 9 and 12kW and larger clusters of several such units can process production volume streams at almost any level.